What is a compact fluorescent light (CFL) bulb?

A compact fluorescent light bulb, or CFL for short, is a CFLs produce light differently than incandescent bulbs. In an incandescent, electric current runs through a wire filament and heats the filament until it starts to glow. In a CFL, an electric current is driven through a tube containing argon and a small amount of mercury vapor. This generates invisible ultraviolet light that excites a fluorescent coating (called phosphor) on the inside of the tube, which then emits visible light. (Source: EnergyStar.gov)